The invention relates to the field of high pressure fluid pumps and, more particularly, to a double-displacement piston-and-cylinder pump with a modular fluid subassembly for operation with paint and other liquids.
Double-displacement pumps, in which fluid is pumped during both strokes of a reciprocating two-stroke cycle, have been used to pressurize paint for airless spraying operations. The pressures required for these purposes put extreme demands on pump mechanisms, however, particularly their fluid sections, leading to high failure rates. They also cause the pumps to be rather large and expensive.
It is extremely difficult and time consuming to service the fluid section of a traditional double-displacement pump under field conditions. Prior fluid sections are not only complex, but also quite sensitive and difficult to replace without sophisticated tools. Replacing the fluid section of an airless paint sprayer typically requires that much of the pump and the fluid section be dismantled and meticulously reassembled. For these reasons, a painter using an airless system ordinarily must deliver the system to a technician for service whenever a failure or internal blockage occurs.
Additionally, it is desirable in some applications to feed paint to a pump from a hopper located above the pump. Diaphragm-type pumps have been used in such situations, but are not suitable for all uses. Piston-and-cylinder pumps are not widely used with hoppers because the excessive length of their fluid sections would require placing a hopper high off the ground, rendering the resulting system unstable.
Pressure control valves, priming valves and other special subsystems are also required in many high pressure pumping applications, increasing the complexity of the pumping system and complicating replacement of its fluid section. Each subsystem is normally connected to the pump housing by one or more separate conduits which must be disconnected and/or dismantled before any components of the fluid section can be removed.
Therefore, it is desirable in many applications to provide a double-displacement piston-and-cylinder type fluid pump that is compact, relatively simple, easy to service (particularly in the field), and can be readily used in a hopper configuration.